Joining Apple, Microsoft, and Facebook, Yahoo has revealed that it received more than 12,000 requests from U.S. law enforcement for user information and affected accounts in the past six months.

The Web pioneer said Monday evening that between December 1, 2012, and May 31, 2013, it received between 12,000 and 13,000 requests for user information, most of which were related to criminal investigations involving fraud, homicide, and kidnapping.

The revelation comes amid a furor that erupted earlier this month over allegations that the National Security Agency has engaged in a sweeping effort to surreptitiously acquire information connected to phone calls and Web usage.

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Meanwhile, Microsoft has disclosed that it received 6,000 to 7,000 criminal and national security warrants, subpoenas, and orders affecting between 31,000 and 32,000 consumer accounts from U.S. governmental entities over the same six-month period.

Initial reports earlier this month in the U.K.-based Guardian and in the Washington Post said U.S. Internet companies allegedly cooperated with an NSA program called PRISM. Yahoo denied the allegations regarding its participation in the program, calling them "categorically false."

While noting that it was prohibited by law from detailing the number of requests made under the Foreign Intelligence Surveillance Act (FISA), Yahoo said it urged the federal government to reconsider declassifying the data.

"Democracy demands accountability," Yahoo CEO Marissa Mayer and general counsel Ron Bell wrote in a Tumblr post published this evening. "Recognizing the important role that Yahoo can play in ensuring accountability, we will issue later this summer our first global law enforcement transparency report, which will cover the first half of the year. We will refresh this report with current statistics twice a year."